Much of this can be dismissed as election-year posturing. Every president finds that the U.S. has limited options in getting China, the world’s second-largest economy and the U.S.’s largest foreign creditor, to adopt market-oriented change. The trick is to get Beijing to see the reform as in its interest, and even then the pace of change is slow.

But political threats, even if they don’t become law or policy, have consequences in Beijing and can backfire in ways that Americans may not appreciate. Beijing is in the throes of its own 2012 leadership change, with top politicians jockeying for power. There’s no election, but public opinion matters. Being seen as close to the U.S. at a time when Washington threatens to whack Beijing is as much a burden for a Chinese politician as being a pal of China would be for an American candidate campaigning in Cleveland.

Cheng Li, a Brookings Institution China scholar, says the threats from Washington have already hurt a U.S. favorite, Vice Premier Wang Qishan, who is viewed as having an outside shot at becoming Chinese premier, the No. 2 position in China. Mr. Wang has argued that China needs to rely more on domestic consumption rather than exports—precisely the U.S. position.

A backlash against U.S. threats could help Bo Xilai, the nationalist party secretary of Chonqqing, a city that recently shut down 13 Wal-Marts for allegedly selling mislabeled pork. Shutting down a supermarket for such a common infraction is unusual.

He’s aiming for a slot on the standing committee of the Politburo. “You’re hurting economic policy makers that have strong ties to the U.S,” Mr. Li said. “It puts them in an awkward position.”

“That in practice would be bad; it would result in a trade war,” said Mr. Huntsman, a former U.S. ambassador to China. “The last thing you need between the two top economies in the world is a trade war, particularly during a recession, for heaven’s sake.”

That’s a shade different from when Mr. Huntsman appeared on Fox News on Sept. 28. “I would sign it, simply because you need to keep pressure on China,” he said at the time. The former governor added that the bill would carry very little meaning, and he believes the country is already working to devalue its currency. Still, he said the law could be used to gain leverage in negotiations with China.

On Monday, Mr. Huntsman said, “I would take that will of Congress and sit down with the leadership of China in the Great Hall of the People, and say, ‘Here’s where my Congress is coming from. We ought to be moving that currency forward just a little bit faster.’ ”